(a) Field of the Invention
The present invention relates to an optical disk and a disk chucking mechanism for holding a disk such as optical disk in a disk recording and/or reproducing apparatus.
(b) Description of the Prior Art
The optical disk heretofore has been proposed as a recording medium for information signal.
The optical disk comprises a disc-shaped disk substrate 101 made of a transparent resin such as polycarbonate and glass and a signal recording layer 102 provided on one main side of the disk substrate 101.
The signal recording layer 102 is formed of a thin film of a metal having a relatively high reflection factor such as aluminium if the disk is a read-only optical disk. The signal recording layer 102 is formed of a thin film of a magnetic material such as perpendicularly magnetically recordable medium if the disk is an optical disk such as magneto-optical disk which information signals can be written to and read from. The surface of the signal recording layer 102 is a signal recording surface 102a. A pregroove is spirally formed in a concentric manner on the signal recording surface 102. If the disk is a read-only optical disk, phase pits are formed along a spiral or concentrical lines on the signal recording surface 102a. An optical disk recording and/or reproducing apparatus is used for writing and/or reading informational signals to and from the optical disk. The optical disk recording and/or reproducing apparatus comprises a rotary drive mechanism for supporting the optical disk to rotate it and an optical pick-up device for irradiating with a flux of light, such as laser beam, the optical disk which is rotated by the rotary drive mechanism.
In the optical disk recording and/or reproducing apparatus, a flux of light from a light source is converged and impinged upon the signal recording surface 102a by the optical pick-up device to perform read/write of informational signals. Irradiation of the optical disk with the flux of light is performed from the other main side of the disk substrate 101. In other words, the light flux from the optical pick-up device transmits through the disk substrate 101 to impinge upon the signal recording surface 102a so that the pregroove is tracked by the optical disc by the optical pick-up device.
The rotary drive mechanism of the disk recording an/or reproducing apparatus has a disk chucking mechanism to hold the optical disk. A disk chucking mechanism including a magnet for attracting disk hub made of a magnetic material, such as iron, nickel or nickel which is secured to an optical disk in the center thereof to hold the optical disk has been proposed to make the apparatus more compact in size.
The disk chucking mechanism comprises a rotary shaft 104a of a spindle motor 104 forming the rotary driving mechanism and a disk table 105 secured to the rotary shaft 104a. The disk table 105 is substantially disc-shaped and is formed in the center thereof with a supporting hole 109 into which the rotary shaft 104a is fitted. That is, the disk table 105 is secured to the rotary shaft 4a by forcedly inserting the rotary shaft 104a into the supporting hole 109.
A flat annular platen 106 is formed on the upper peripheral edge of the disk table 105. The platen 106 abuts upon the disk substrate 101 of the optical disk to restrict the height position of the optical disk, that is, the position of the disk substrate 101 in a direction perpendicular to the main surface thereof. The disk table 105 is provided with a projecting spindle shaft 107 on the upper side thereof. The spindle shaft 107 projects upward beyond the platen 106. An annular magnet 108 is provided inside of the platen 106, that is, around the spindle shaft 107. The upper side of the magnet 108 is not projected upwardly beyond the platen 106.
A disk hub 103 is secured to the disk substrate 101 of the optical disk in the center thereof. The disk hub 103 is formed of a magnetic material and is disc-shaped. The disk hub is fitted into a hub mounting hole 101 bored in the center of the disk substrate 101 and is firmly secured to the disk substrate 101 by bonding means such as adhesive. The disk hub 103 is bored with a center hole 110 in the center thereof into which the spindle shaft 107 is inserted.
In order to hold the thus formed optical disk by the disk chucking mechanism, the spindle shaft 107 is inserted into the center hole 110 of the optical disk and the disk hub 1 is placed upon the disk table 5. Then, the magnet 108 attracts the plate 103 so that the peripheral edge of the disk hub 103 is brought into a pressure contact with the plate 106. The optical disk which is held by the disk chucking mechanism in such a manner is restricted in height position relative to the platen 106 and is restricted in position in a horizontal direction, that is, in a radial direction of the disk substrate 101 relative to the spindle shaft 107 so that the optical disk is not offset from the rotary shaft 104a.
If the center of rotation of the rotary shaft 104a of the motor 104 is offset from the center of curvature of the pregroove formed on the signal recording surface 102a of the optical disk, the pregroove of the optical disk would be cyclically moved in a radial direction of the optical disk when the optical disk held by the disk chucking mechanism is rotated. If the movement of such pregroove is large, it will become difficult to irradiate the pregroove with the flux of light by the optical pick-up device, resulting in difficulty to perform a good writing and/or reading of the informational signal.
The position of the optical disk in a horizontal direction is restricted by the fitting of the spindle shaft 107 into the center hole 110 in the above-mentioned optical disk and the disk chucking mechanism. Accordingly, it is necessary to align the center of the center hole 110 with the center of curvature of the pregroove of the optical disk when the disk hub 103 is mounted upon the disk substrate 101.
Accordingly, it is necessary to mount the disk hub 103 on the disk substrate 101 after positioning the disk hub 103 relative to the pregroove formed on the disk in order to manufacture the optical disk. The manufacturing process is complicated.
In order to positively hold the disk in such a manner that the platen 106 and disk substrate 101 are not slid with each other when the disk is rotated, the magnetic force of the magnet 108 should be sufficiently strong in the above mentioned chucking mechanism.
If the magnet 108 has a sufficient magnetic force, it would become larger in size and the disk table would also become larger in size. It will become difficult to miniaturize the structure of the disk player apparatus.
If the magnetic force of the magnet 108 is made excessively strong, the magnetic flux emitted form the magnet 108 may be leaked to the signal recording surface 102a of the disk. If the magnetic flux from the magnet 108 is leaked to the signal recording surface 102a of the disk, the signal recording layer 102 of the disk is influenced by the magnetic flux leaked from the magnet 108, resulting in that good writing and/or reading of informational signals becomes impossible.